Electrical network analysis relies on measurements of amplitude and phase (or group delay) of transmitted or reflected electrical signals. For optical networks the measurements can be more complicated due to the polarization states of optical signals within the optical networks. The characterization of optical networks requires a measurement of phase and amplitude, and also a measurement of phase and amplitude dependence on the polarization state. All parameters are typically tested versus optical frequency.
The complexity of the characterization of optical networks has led to the development of multiple instruments that perform a variety of measurements. For example, a tunable laser and a power meter can be used to measure an amplitude response of an optical network. A tunable laser, a polarization controller and a power meter can be used to measure an amplitude dependence on the polarization state, typically quantified by a polarization dependent loss (PDL). The PDL is expressed by a difference between the maximum and the minimum transmission (or reflection).
A tunable laser and polarimeter can be used to directly measure a Jones matrix. Eigen-analysis of Jones matrices provides in turn information about the PDL and a polarization dependence of the group delay often described by a differential group delay (DGD). The DGD is expressed by a difference between the maximum and the minimum group delay. In another technique, often referred to as the phase shift method, an intensity-modulated tunable laser and a high-speed synchronous detector allowed for a direct measurement of the group delay and the amplitude. The phase shift method of measuring dispersion provides a correct estimate of the group delay when the device under test (DUT) does not contain polarization maintaining fiber (linear birefringence). However, in this method, the polarization rotation in the polarization maintaining fiber corrupts the group delay measurements. It is also known in the prior art to obtain most of the foregoing measurements with a single instrument including a tunable laser, an interferometer and a polarization-resolving module that is realized by a polarization diversity receiver or a tunable laser polarization controller. An example of such an instrument is the Agilent 81910A Photonic All-Parameter Analyzer.
However, the analysis techniques using an instrument such as the 81910A Photonic Parameter Analyzer were adapted from techniques used with precursor instruments. For example, the DGD estimation obtained with this type of instrument is based on the Jones matrix eigen-analysis. The PDL estimation is based on the Jones matrix eigen-analysis or on the Mueller matrix method. Furthermore, the amplitude and phase are estimated directly from the phase and amplitude of the detected interferometric signals. Thus, any instabilities of the interferometer or the phase noise of the laser source affect the precision of the measurements. This is particularly inconvenient because of the inherent sensitivity of the measurements to vibration and temperature fluctuations.